Ocean Acidification Mitigates the Negative Effects of Increased Sea Temperatures on the Biomineralization and Crystalline Ultrastructure of Mytilus

Abstract

Negative impacts of global climate change are predicted for a range of taxa. Projections predict marked increases in sea surface temperatures and ocean acidification (OA), arguably placing calcifying organisms at most risk. While detrimental impacts of environmental change on the growth and ultrastructure of bivalve mollusk shells have been shown, rapid and diel fluctuations in pH typical of coastal systems are often not considered. Mytilus edulis, an economically important marine calcifier vulnerable to climate change, were exposed to current and future OA (380 and 1000 ppm pCO 2), warming (17 and 20 • C), and ocean acidification and warming (OAW) scenarios in a seawater system incorporating natural fluctuations in pH. Both macroscopic morphometrics (length, width, height, volume) and microscopic changes in the crystalline structure of shells (ultrastructure) using electron backscatter diffraction (EBSD) were measured over time. Increases in seawater temperature and OAW scenarios led to increased and decreased shell growth respectively and on marginal changes in cavity volumes. Shell crystal matrices became disordered shifting toward preferred alignment under elevated temperatures indicating restricted growth, whereas Mytilus grown under OAW scenarios maintained single crystal fabrics suggesting OA may ameliorate some of the negative consequences of temperature increases. However, both elevated temperature and OAW led to significant increases in crystal size (grain area and diameter) and misorientation frequencies, suggesting a propensity toward increased shell brittleness. Results suggest adult Mytilus may become more susceptible to biological determinants of survival in the future, altering ecosystem structure and functioning.

Combined effects of ocean warming and acidification on the larval stages of the European abalone Haliotis tuberculata

“…The combined impacts of OA and OW have been addressed with contrasting responses, such that the effects of OA and OW are either exacerbated (e.g., Di Santo 2015;D'Amario et al, 2020;Zittier et al 2018;Rodolfo-Metalpa et al, 2011) or ameliorated (e.g., Kroeker et al 2014;Knights et al, 2020;García et al, 2015;Jiang et al, 2018) in the presence of the other stressor (). Meta-analyses have suggested that the combined impacts of OA and OW on species physiology are especially devastating for the larval stages of many species (Przeslawski et al, 2015;Kroeker et al, 2013), presenting a major bottleneck for population persistence under changing oceanic conditions (Przeslawski et al, 2015).…”

An Assessment of the Potential Value for Climate Remediation of Ocean Calcifiers in Sequestration of Atmospheric Carbon

“…Another study with Mytilus, which used a similarly extreme upper CO2 level, found that the resultant acidification (or, as we prefer, reduced alkalinity) suggests a complex relationship between calcification and the various active components of climate change that might ease the negative effects of increased sea temperatures on biomineralisation in the mussel [37]. Even greater complexities become evident in organisms, like calcifying phytoplankton (coccolithophores), that bring photosynthesis into the mix of variables [38].…”

Saving the planet with appropriate biotechnology: 3. The high seas solution

“…Fitzer et al (2016) have demonstrated significant changes in the hydrated and dehydrated forms of amorphous calcium carbonate in the crystalline layers of mussel (Mytilus edulis) shells cultured under acidification conditions. However, there is evidence that, in Mytilus, acidification eases the negative effects of increased sea temperatures on biomineralization, suggesting a complex relationship between calcification and the various components of climate change (Knights et al, 2020). Adverse effects of present day ocean acidification are clearly seen to impact the viability of symbiotic algae of coral and giant clams, and in those cases, too, are interwoven with elevated temperatures and light levels in relatively shallow tropical waters.…”